It is known to make a tubing elbow by separately deep-drawing each of two identical metal plates between an upwardly concave lower die assembly and a downwardly convex upper die assembly. The two plates are identically deformed between the two die assemblies so that each becomes an upwardly open trough arcuate in a horizontal plane. One of these troughs is reversed and placed on top of the other trough, so as to open downwardly against it, and the mating edges are welded together. This method is described in German Pat. No. 1,953,387.
Normally the die havles each have a single integral piece defining the respective drawing surface, that is the upper surface which is upwardly concave of the lower die and the lower surface with is downwardly convex of the upper die. It has been standard practice to make these dies so as to produce tubing elbows having arc lengths of 90.degree.. When a tubing elbow of shorter arc length is needed a shorter plate is deep-drawn by the same die assembly, or a 90.degree. elbow is cut down.
When it is necessary to use such a tubing elbow in a highly critical application, as in the cooling coil of a nuclear reactor, it is essential that a perfect weld or joint be formed between each end of the tubing elbow and the respective pipe. Such a perfect joint can normally be formed relatively easily with a 90.degree. elbow, as the die is normally set up to produce a perfectly round cross section at each outer end of the elbow. When, however, an elbow of shorter arc length is needed, it is much more difficult to obtain the required perfect weld, as the cross section of the tubing elbow invariably varies somewhat from the perfectly circular throughout the length of the elbow.
Thus it is normally necessary to use separate individual dies for each tubing elbow of a different arc length. In normal practice this requires the manufacturer to have on hand for each pipe diameter a complete set of elbow dies. These dies are enormously expensive, as they are made of tool steel and must normally be machined and produced by hand, so that as a result the cost of tubing elbows produced thereby becomes quite elevated.